Chapter 1: The Characeae Plant

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Lamprothamnium in 1916 to avoid a nomenclatural conflict with a flowering plant genus
(Groves 1916). Other species of Lamprothamnium were added over time, so that in 2010 the
genus had approximately seven recognised species. All members of the genus
Lamprothamnium have ecorticate internodes and branchlets (similar to C. australis), but
differ in the presence of downward pointing stipulodes and angular whorls of bract cells at
the branchlet nodes (spreading, verticillate bract cells) (Fig. 1.7a). Many specimens have
distinctive, spherical white bulbils at the rhizoid nodes (McNicol 1907; Ophel 1947). These
bulbils are full of starch grains, and they allow the plant to persist when it is unable to
photosynthesise, and to regenerate when the vegetative axis is uprooted or destroyed. There is
a high degree of morphological similarity among species of Lamprothamnium (García and
Casanova 2004), and the most recent taxonomic treatments use the arrangement of the
reproductive organs as a guide for distinguishing different species (Casanova et al. 2011).
Lamprothamnium papulosum has antheridia and oogonia together on the branchlet nodes,
with the antheridium above the oogonium (Fig. 1.7e). There are a number of species of
Lamprothamnium in Australia, many of which were amalgamated with European L.
papulosum in the past (Wood 1972), however none of them exhibit the particular
arrangement of reproductive organs found in that species. The most commonly mentioned
species is L. macropogon (A. Braun) I.L. Ophel. In non-reproductive plants of L.
macropogon there can be a whorl of upward-pointing stipulodes within the branchlet whorl
(Ophel 1947). The oogonia are clustered inside the base of the branchlet whorl, and one or
two can be found on the first branchlet node (Fig. 1.7b, c). The antheridia are rarely present
singly inside the branchlet whorls (jammed in with the oogonia), they are mostly confined to
the first and second branchlet nodes (Fig. 1.7d). Male and female gametangia occur together
(side by side) at the same branchlet node rarely. The shoots of species of Lamprothamnium
often have a dense ‘fox-tail’ appearance (‘alopecuroid’) because the upper internodes are
short and the branchlets, stipulodes and bract cells overlap. There are several additional taxa
of Lamprothamnium similar to L. papulosum and L. macropogon, including L. hansenii in
which the branchlet segments are rather stout and constricted at the nodes (Wood 1965), L.
heraldii which is dioecious (García and Casanova 2004), L. papulosum vars toletanus,
carrissoi and aragonense from Spain (Cirujano et al. 2008) and L. sonderi in Germany
(Schubert and Blindow 2003), but these are less frequently used for physiological studies.
Additional, undescribed species of Lamprothamnium exist in Australia.